The present invention relates generally to fuel vapor emission control in vehicles having internal combustion engines. More particularly, the invention relates to a system and method for removing evaporative emissions from the intake manifold of an internal combustion engine.
Vehicles having internal combustion engines are known to release disproportionate amounts of hydrocarbons during engine cold starting and vehicle refueling. During cold starting, for example, because a stoichiometric air/fuel ratio is difficult to achieve, a higher proportion of unburned fuel vapor is delivered to the vehicle""s catalytic converter thus resulting in higher concentration of hydrocarbon molecules released into the atmosphere. Similarly, during refueling, unburned fuel vapors containing such hydrocarbons are released from the vehicle""s fuel tank when the fuel tank cap is removed.
As such, vehicles have been designed to include various features for minimizing the release of fuel vapor emissions during vehicle start-up and refueling. Examples of such systems are disclosed in U.S. Pat. Nos. RE 36,737, 5,924,410 and 5,957,114, which are all assigned to the assignee of the present invention. Another such system is described in co-pending U.S. application Ser. No. 09/634,618, which is also assigned to the assignee of the present invention and is hereby incorporated by reference in its entirety. The system disclosed therein includes a fuel tank that is sealed-off under vacuum when the vehicle is not being refueled. When the vehicle is refueled, a refueling detection device activates a fuel vapor valve, which is used to divert accumulated fuel vapors from the fuel tank to a fuel vapor absorption device.
A limitation of such systems, however, is that the trapping of fuel emissions is limited to refueling and engine start-up. Such systems, for example, do not take into account unburned fuel vapors that escape through other parts of the engine. One such part is the intake manifold, wherein unburned fuel and associated vapors are known to accumulate.
Accordingly, and further in light of increasingly stringent environmental standards, the inventor herein has recognized the need to minimize the amount of unburned fuel vapors accumulating in the engine""s intake manifold.
The aforedescribed limitations and inadequacies of conventional fuel evaporative emission controls systems and methods are substantially overcome by the present invention, in which a method is provided for removing fuel vapors from an intake manifold of an internal combustion engine. In accordance with a preferred method of the present invention, the method includes the steps of storing a vacuum in a vacuum storage device coupled to the intake manifold and applying the stored vacuum to the intake manifold to remove the vapors from the intake manifold. Further, the method includes the steps of storing the vapors in the vacuum storage device to prevent the release of the vapors into the atmosphere and transferring the stored vapors to an on-board fuel vapor recovery system. Preferably, the vacuum storage device is the vehicle""fuel tank and the transfer of the stored emissions is performed prior to refueling of the vehicle.
An advantage of the above method is that the amount of fuel vapors accumulated in the engine""s intake manifold is significantly reduced, thereby preventing the release of residual gases into the atmosphere. Such a method is thus used to control fuel evaporative emissions originating from a source other than those addressed by the prior art methods directed at minimizing emissions during engine start-up and refueling.
In accordance with another aspect of the present invention, a corresponding system is provided for minimizing fuel evaporative emissions that accumulate in the intake manifold of an internal combustion engine. The system includes a vacuum storage device, such as a vehicle fuel tank, an electronically controlled shut-down valve disposed between the vacuum storage device and the intake manifold and interconnecting the vacuum storage device and the intake manifold; and an electronic controller coupled to the shut-down valve and operable to evacuate the intake manifold of fuel evaporative emissions at a predetermined time. Advantageously, the system is further provided with a refueling/interlock valve that allows the transfer of the stored fuel vapors to an on-board fuel vapor recovery system.
Still further, in accordance with yet another aspect of the present invention, an article of manufacture is disclosed for minimizing evaporative fuel emissions of a vehicle having an internal combustion engine. The article of manufacture includes a computer usable medium and a computer readable program code embodied in the computer usable medium for directing the computer to perform the steps of storing a vacuum in a vacuum storage device coupled to the engine""s intake manifold and applying the stored vacuum to the intake manifold to evacuate the vapors from the intake manifold and into the vacuum storage device.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.